Scopolamine impairs human recognition memory: Data and modeling.

Eight subjects studied a set of complex visual images after administration of 0.4 mg scopolamine. Another 8 subjects performed the same task without drug administration. On a subsequent item recognition test, subjects rated, on a 5-point scale, their confidence that the studied pictures and an equal number of unstudied lures were actually presented. Results showed that scopolamine affected responses to studied items, but not unstudied lures, demonstrating an unambiguous effect of scopolamine on recognition memory. To describe the scopolamine-injected subjects' data, the authors constructed a new model of 2-process recognition that includes the A. P. Yonelinas (1994) model as a limiting case. The model analysis suggests that scopolamine affected both familiarity and recollection. In particular, scopolamine did not affect the frequency with which recollection took place, but rather, affected the amount of recollected information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Involvement of the olfactory bulb in consolidation processes associated with long-term memory in rats.

In a daily training paradigm, rats were trained to discriminate between spatially distinct electrical stimulations delivered to one olfactory bulb. Xylocaine injections were used to disrupt the olfactory bulb functioning in the region close to the electrode tips for 1 hr after each training session. The treatment started either just after the session or 2 hrs later. When compared with the performance of saline-injected rats, the performance of Xylocaine-injected rats was unimpaired except when the treatment started just after the daily session. In that case, acquisition of the task was slightly altered, and retention over a 5-day period was dramatically impaired. It is concluded that, within 1 hr following training, the olfactory bulb is engaged in consolidation processes critical for long-term retention of learned olfactory cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Scopolamine impairs object exploration but not habituation in rats

Memory of a novel object was examined in saline (Sal) and scopolamine (Scopo) treated rats (1.0 mg/kg). Scopo rats showed lower overall exploration time than Sal rats, resulting mainly from shorter durations per contact. In a second exposure to the same object, after 1 min or 20 min interval, both groups displayed marked decrease of exploration indicating between-session habituation. The shorter time spent by Scopo rats on investigation of an object during a single approach might be interpreted as a deficit in maintenance of attention. Nevertheless, Scopo rats were able to acquire sufficient information for the retention during 20 min interval, as indicated by habituation, which is an elementary index of memory.     

The importance of calmodulin in the accessory olfactory bulb in the formation of an olfactory memory in mice

Female mice form an olfactory memory to the pheromones of the mating male, during a critical period after mating. Failure to form this memory results in the male being treated as strange, and hence, his pheromones block pregnancy. Previous studies have shown that formation of this memory is dependent on synaptic mechanisms in the accessory olfactory bulb. A number of studies have pointed to calmodulin as a critical mediator of synaptic plasticity. In this study we have examined the effects of local infusions of drugs which block calmodulin-regulated processes, into the accessory olfactory bulb on the formation of this memory. Infusions of the calmodulin antagonist calmidazolium during the critical period prevented memory formation. However, the specific inhibitor of calcium/calmodulin-dependent protein kinase II, KN-62, or the selective inhibitor of calcium/calmodulin-dependent protein phosphatase 2B (calcineurin), FK506, was without effect on memory formation at any of the doses used. Instead of preventing memory formation, FK506 permitted the formation of a non-selective memory to strange male pheromones in the presence of mating, although FK506 alone could not induce a memory without the occurrence of mating. These results suggest that calmodulin in the accessory olfactory bulb is important in the formation of the olfactory memory to male pheromones. However, memory formation may be independent of calmodulin-kinase II. Calcineurin may play a role in processes antagonizing memory formation.     

Adolescent cocaine residually impairs working memory and enhances fear memory in rats.

The residual effects of cocaine during adolescence on memory in male young adult rats were studied. Animals were injected with 20 mg/kg cocaine on postnatal Days 28 through 35, whereas lab-chow (LC) and pair-fed (PF) control subjects received saline. Assessment of spatial working and long-term memory in the Morris water maze, and 72-h retention of an inhibitory avoidance task was conducted at about 5 and 9 weeks postcocaine, respectively. Relative to PF control subjects, cocaine-treated subjects showed impairments in the water maze when required to swim to the hidden platform placed in a quadrant diagonal from the location of its original location (i.e., on reversal learning). These same drug-treated animals, however, exhibited enhanced inhibitory avoidance retention relative to both control groups. These seemingly disparate findings are seen as being consistent with previous data showing that cocaine during adolescence residually impairs spatial memory and leads to enhanced fear responses. Moreover, when taken with previous findings from our laboratory, the present water maze data indicate that the deleterious effects of cocaine, when administered during adolescence, is delayed until 5 weeks after initiation of abstinence. It is speculated that alterations to limbic circuitry, especially those associated with the amygdala, account for the behavioral results observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Antagonism of NMDA receptors impairs acquisition but not retention of olfactory memory.

Examined the effect of chronic intraventricular administration of D-amino-phosphono-valeric acid (AP5), a competitive NMDA receptor antagonist, on olfactory discrimination and avoidance learning. 20 rats previously trained to solve a series of discriminations between 2 simultaneously presented odors were infused with either 20 mM D-AP5 or saline for 14 days. An important and unusual feature of the paradigm was that it permitted a comparison of drug effects on acquisition of new discriminations vs retention of old ones. Animals treated with AP5 made significantly more errors than did controls in acquiring discriminations between low-intensity odors presented with long intertrial intervals (ITIs). However, no deficit was observed when short ITIs or strong odors were used. Animals treated with AP5 had no difficulty in recognizing odors on which they were trained before administration of the drug. After exhaustion of the pumps, performance of the AP5 group was indistinguishable from that of the control group. One-way active avoidance learning was not affected by chronic infusion of AP5. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dopaminergic modulation of olfactory bulb processing affects odor discrimination learning in rats.

Olfactory behavioral studies have shown that, when modulated through systemic injections, D1 and D2 receptors have opposing effects on odor discrimination learning. In the present study, cannulated male Sprague–Dawley rats were used to investigate how the modulation of these 2 types of dopaminergic receptors through direct infusion of D1/D2 agonists and antagonists into the olfactory bulb affect olfactory perception. Dopaminergic modulation was locally altered by manipulations of D1 (agonist SKF 82958: 14.6, 43.8, & 143.6 mM; antagonist SCH-23390: 13.4, 40.1, & 60.1 mM) and D2 (agonists quinpirole: 78.2, 117.3, & 156.4 mM; antagonist sulpiride: 0.3, 0.9, & 2.9 mM) receptors during a simultaneous odor discrimination task. The authors found that modulation of D2, but not D1, receptors significantly affected rats’ odor discrimination performance. A significant positive correlation between blockade of D2 receptors and discrimination performance, as well as a significant negative correlation between D2 receptor activation and discrimination performance, was observed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of the olfactory bulb in limbic mechanisms.

Reviews recent data obtained after peripheral olfactory system damage which, when compared with bulbectomy data, suggest that the olfactory bulb has certain general modulatory functions in addition to its specific sensory role as initial processor of olfactory information. It is proposed that the olfactory bulb is involved in a forebrain arousal mechanism comprised mainly of hypothalamus and limbic system. Behavioral and electrophysiological evidence is discussed that supports the idea that the olfactory bulb may modulate the excitability of forebrain regions. Anatomical details of the system are considered, and its relationship to reinforcement mechanisms and to A. Routtenberg's (see PA, Vol 42:5112 and 47:244) Arousal System II is outlined. (5 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Two circuits to convert short-term memory into long-term memory

In this prospective study we tested the hypothesis that atropine administration, which is known to increase heart rate and cardiac output in infants, will result in a faster onset of neuromuscular block with atracurium. Thirty infants scheduled for elective surgery had anaesthesia induced with nitrous oxide and halothane. Fifteen patients were given atropine and 15 patients acted as controls. All the infants were given atracurium 0.5 mg.kg-1, and neuromuscular block was recorded with the Datex 221 neuromuscular transmission monitor. Although atropine caused an increase in heart rate compared to the control group (median 164 [range 151-182] vs 120 [98-160]min-1 P < 0.0001), there was not a statistically significant difference in the onset of neuromuscular block between the two groups. We conclude that onset of neuromuscular block after atracurium is determined mainly by noncirculatory factors and less by the circulation time to the muscle. The effect of atropine on the time course of neuromuscular block might be different with faster acting neuromuscular blockers.     

Detection and discrimination of carvone enantiomers in rats with olfactory bulb lesions

Rats with lesions of dorsal and dorsolateral bulbar sites known to be differentially responsive to carvone enantiomers were tested for their ability to detect (+)-carvone, to discriminate between (+)-carvone from (-)-carvone, and to discriminate (+)-carvone from mixtures of both enantiomers after they had been pre-trained or not pre-trained on these tasks prior to surgery. In postoperative tests, rats pre-trained on the enantiomer discrimination problems made somewhat fewer errors than those not pre-trained, but experimental rats performed as well as controls (those that had one intact olfactory bulb) within both conditions and on each task. These results indicate that removal of most bulbar sites known to be differentially responsive to carvone enantiomers and the consequent disruption of normal patterns of bulbar input produced in response to carvones are largely without effect on the ability of rats to discriminate between these odors.     

Some behavioral effects of olfactory bulb damage in the rat.

Conducted 5 experiments in which male Holtzman rats (N = 50) with either olfactory bulb or septal lesions were tested on position-habit reversal, nonappetitive passive-avoidance, 1-way avoidance, and 2-way avoidance tasks. Ss with septal damage exhibited the expected behavioral abnormalities on all tasks. Ss with bulbar damage were deficient on 1-way avoidance, were facilitated on 2-way avoidance, and could not be distinguished from the normal Ss on the other 2 tasks. (20 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Microinjection of morphine into the nucleus accumbens impairs contextual learning in rats.

A unilateral microinjection of morphine into the amygdala impaired fear conditioning to both a conditioned stimulus (CS) paired with shock and the context where shock occurred, whereas a microinjection of morphine into the nucleus accumbens (NA) spared fear conditioning to the CS but impaired, in a dose-dependent and receptor-specific manner, fear conditioning to the context. Morphine in the NA also spared extinction and latent inhibition of a CS but abolished the context specificity of these effects and eliminated the increase in discriminability that results from preexposure to a to-be-shocked context. The results identify a role for the NA in the processes by which rats learn about a context and are discussed in terms of an opioid disruption of either within-context associations or of attentional processes that contribute to such associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurocalcin immunoreactivity in the rat main olfactory bulb

The morphological characteristics and distribution of neurocalcin (NC)-immunoreactive elements were studied in the rat main olfactory bulb (OB) using a polyclonal antibody and the avidin-biotin immunoperoxidase method. NC-positive elements were abundant in the glomerular layer (GL), where numerous immunostained external tufted cells and periglomerular cells were detected. Other less abundant NC-immunolabeled populations included middle and internal tufted cells, Van Gehuchten cells, horizontal cells, vertical cells of Cajal, deep short-axon cells and granule cells. This study demonstrates the presence of NC immunoreactivity in subsets of different neuronal types in the rat main OB. This calcium-binding protein has been found in interneurons, and no evidence of immunoreactivity to NC is detected in projecting neurons. Despite the large population of labeled external tufted cells, most of them belong according to morphological criteria to the local circuit group and some others to those with interbulbar and/or intrabulbar connections. The identification of neuronal subpopulations expressing NC provides a further characterization and shows the existence of biochemical differences within morphologically identical neurons. Thus, this marker may be a useful tool in unravelling the circuitries of the rodent OB in both normal and experimental conditions. The exact physiological function of NC in the olfactory system remains unknown. On the basis of similarities to recoverin, it could be involved in mechanisms responsible for sensory adaptation. Additionally, its calcium-binding abilities may contribute to improve the temporal precision of stimuli transmission, or be concerned with general calcium-related events occurring in specific interneuronal groups.     

Short-lasting exposure to one odour decreases general reactivity in the olfactory bulb of adult rats

We investigated in adult rats whether a relatively short exposure to a novel odour can lead to changes in reactivity of olfactory bulb principal neurons. Naive rats were exposed to isoamyl acetate for 20 min per day either for 6 consecutive days or for a single 20-min exposure. Control group was non-exposed. Under anaesthesia, responsiveness of each recorded single mitral/tufted cell was tested towards isoamyl acetate and four other odours. Results show that the proportion of responding cells in the exposed groups decreased drastically when compared to controls. In the two experimental groups recorded 24 h following the last exposure, mitral/tufted cells show a significant decrease in the number of excitatory responses. In parallel, the number of non-responsive cells increased by at least a fourfold factor. This decrease in reactivity was not selective towards the odour used during the exposure but concerned any of the five test-odours presented during recordings. Finally, this lower responsiveness was long lasting as it was still observed 10 days after the end of the last exposure. This preliminary study points out the importance of even limited sensory experience in neural representation of odours.     

Binomial variability in short-term memory.

Experiments in short-term memory usually collect binary data, e.g., an item is either correctly recalled or not. If the probability of recall is constant for Ss and/or items under a given condition, the proportion based on n observations can be transformed to angles by the arcsin transformation and will have variance 1/n. Violations of the assumptions are discussed and different strategies for pooling are assessed by conventional analysis of variance. Illustrative experiments with distractor and probe techniques, paired-associates and serial presentation, and single-trial free recall are briefly presented. The correspondence between observed and expected results seems good; apparently considerable latitude is possible in pooling Ss or items in data analyses of experiments in short-term memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Slope analysis in short-term memory.

Presents procedures for transforming dichotomously scored data from short-term memory experiments into slope measures for evaluation by analysis of variance techniques. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Binding in short-term visual memory.

The integration of complex information in working memory, and its effect on capacity, shape the limits of conscious cognition. The literature conflicts on whether short-term visual memory represents information as integrated objects. A change-detection paradigm using objects defined by color with location or shape was used to investigate binding in short-term visual memory. Results showed that features from the same dimension compete for capacity, whereas features from different dimensions can be stored in parallel. Binding between these features can occur, but focused attention is required to create and maintain the binding over time, and this integrated format is vulnerable to interference. In the proposed model, working memory capacity is limited both by the independent capacity of simple feature stores and by demands on attention networks that integrate this distributed information into complex but unified thought objects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Proactive interference effects on short-term memory in rats: II. Effects in young and aged rats.

Whether the short-term memory impairments of aged rats in an operant delayed-matching task is attributable to increased susceptibility to proactive interference (PI) was tested. Groups of young and aged rats were trained on the task, and the previously reported delay-dependent deficit of aged rats was replicated. The aged rats showed a significantly greater decline in performance on previous-response-opposite trials compared with previous-response-same trials than did young rats, when tested over the same range of delay intervals, suggesting a higher sensitivity to PI. However, this effect was established against a higher overall baseline performance of the young animals on both types of trials. When the young and aged animals were equated for performance on previous-response-same trials (by increasing the range of delay intervals used for testing the young animals), the interaction effect was abolished. Thus, the delay-dependent deficits of aged rats are independent of their sensitivity to PI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of variable periods of functional deprivation on olfactory bulb development in rats

Dramatic alterations occur in the developing olfactory bulb when air flow is reduced through one-half of the nasal cavity. Naris closure on the day after the day of birth (P1) in rats, for example, results in reduced cell survival in the ipsilateral bulb by P20 and a substantial (25%) decrease in bulb size by P30. Almost immediate changes in protein synthesis and cell metabolism are also observed, and one prevalent theory suggests that these changes may be important in specifying which cells are subsequently eliminated. In the present study we used a reversible technique for unilateral naris closure to examine the sensitive period for the effects of olfactory deprivation on bulb size and cell survival. This technique involves the insertion of removable plugs into a rat pup's external naris. We occluded the naris for increasing periods of time (P1-P10, P1-P15, or P1-P20), reared all animals to P30, and measured volumes of bulb laminae. In addition, we examined the duration of naris closure needed to affect cell survival by injecting animals with the thymidine analogue bromodeoxyuridine to label cells born soon after the onset of olfactory deprivation. Results indicate that relatively long periods of naris occlusion (P1-P15 or longer) are required to produce a substantial reduction in experimental bulb size. Cell survival was decreased following olfactory deprivation from P1 to P10, but not after deprivation from P1 to P3. These data support the hypothesis that changes that occur within 48 h of naris closure are not sufficient to affect cell survival.     

Androgen deprivation impairs memory in older men.

Androgen deprivation leads to a profound loss of synaptic density in the hippocampus and changes in learning and memory in animal models. The authors examined group differences in verbal memory between men on androgen deprivation therapy (ADT), a commonly used treatment for prostate cancer, and healthy men. The authors found that men on ADT have a specific impairment of retention but normal encoding and retrieval processes on a word list-learning task. Speed and accuracy for both perceptual and semantic encoding, as well as retrieval at a very short retention interval, were not affected; however, recognition fell to chance after a 2-min retention interval in men on ADT. Healthy men showed only moderate forgetting, and performance was still above chance at 12 min. This pattern of preserved encoding and retrieval but impaired retention suggests that androgens play a role in hippocampally mediated memory processes, possibly having a specific affect on consolidation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)